userfaultfd_read_block.c

#define _GNU_SOURCE
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <assert.h>
#include <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <time.h>
#include <sys/mman.h>
#include <sys/syscall.h>
#include <sys/ioctl.h>
#include <pthread.h>
#include <linux/userfaultfd.h>

struct test_data {
  int uffd;
  int read_res;
  int read_errno;
};

static void *uffd_read_thread(void *arg)
{
        struct test_data* data = (struct test_data*)arg;
        int res;

        struct uffd_msg msg;
        res = read(data->uffd, &msg, sizeof(msg));
        data->read_res = res;
        data->read_errno = errno;

        return NULL;
}

static int test_userfaultfd_closing(int close_timeout)
{
        struct test_data data;
        struct uffdio_api uffdio_api;
        pthread_t read_thread;
        int uffd = syscall(__NR_userfaultfd, 0);
        assert(uffd != -1);

        uffdio_api.api = UFFD_API;
        uffdio_api.features = 0;
        assert(ioctl(uffd, UFFDIO_API, &uffdio_api) != -1);

        data.uffd = uffd;

        assert(pthread_create(&read_thread, NULL,
                              uffd_read_thread, (void *)&data) == 0);

        /* Wait for the other thread to enter the read */
        usleep(1000*close_timeout);
        assert(close(uffd) != -1);
        assert(fcntl(uffd, F_GETFD) == -1 && errno == EBADF);

        pthread_join(read_thread, NULL);

        /* We should be woken up about the fd being closed */
        fprintf(stderr, "read_res = %d, read_errno=%d\n",
                        data.read_res, data.read_errno);
        assert(data.read_res == -1);
        return 0;
}

int main(int argc, char **argv)
{
       if (argc < 2) {
        return 1;
       }
       return test_userfaultfd_closing(atoi(argv[1]));
}